In 1977, Dr. Andreas Gruntzig first used a balloon-tipped flexible catheter to percutaneously dilate a region of stenosis within the coronary artery of a patient suffering from atherosclerotic heart disease. Since that time, the use of percutaneous transluminal coronary angioplasty has increased exponentially, and over the past eight to ten years, has become a routine procedure in many major medical centers throughout the world. With the advent of improved technology and operator skill, the indications for and use of this procedure have increased substantially. With such increased use, a need has developed for systems which have a low "crossing profile" (cross-sectional diameter of the balloon in the deflated state), low "shaft profile" (cross-sectional diameter of the catheter body), high "pushability" (resistance to collapse along the axial direction) and high "steerability" (directional control within the course of a body vessel). The reasons are as follows.
Lower profile systems offer several advantages over their larger profile counterparts. Systems with lower crossing profiles offer lowered resistance during advancement within the vasculature, and consequently offer greater ease of installation across the confines of intravascular lesions relative to comparable systems of larger crossing profile. A further advantage is that these systems can be used in critical lesions that cannot accommodate catheters of larger profile crossing profile. Systems with lower shaft profiles provoke less interruption to the surrounding flow of fluids (i.e., blood, blood substitutes, contrast medium and medications) following introduction within the vasculature, and are thus less prone to provoke ischemia, impair the delivery of medications and compromise the resolution of intraoperative angiography, relative to comparable systems of larger crossing profile.
Systems with greater pushability are easier to advance through regions of the vasculature that provoke resistance to catheter introduction relative to systems that provide inferior pushability. For purposes of this discussion, the term "pushability" will be used to denote the degree to which the catheter component of the system can be advanced into the vasculature without experiencing axial compression. Axial compression is the twisting, gathering or any other form of bending back of the balloon or shaft along the longitudinal axis of the system, which might occur in response to friction from the vasculature or, in the case of percutaneous transluminal coronary angioplasty, in response to friction from the guiding catheter which conducts the angioplasty catheter-guidewire system from the vascular access site to the origin of the coronary artery requiring treatment.
Systems with greater steerability are easier to direct through tortuous regions of the vasculature requiring treatment relative to those with less steerability, and thus offer a variety of features to balloon-mediated intravascular dilatation, including enhanced safety, facility and efficiency. Thus, the ease of positioning a catheter system for use varies directly with its "steerability" and "pushability," and inversely with the "crossing" and shaft profile of the system.
The shaft profile of a catheter-guidewire system varies with the number of channels contained within the catheter shaft. Other things being equal, multi-channel systems have larger profile shafts relative to single-channel systems. The pushability of a catheter system varies directly with the axial rigidity of the structural element (typically the guidewire mandrel or catheter body) that provides axial support to the system. Guidewire mandrels are constructed of stainless steel, which is less compliant than the polymeric materials commonly used in the construction of catheter bodies. For this reason, systems that rely upon the guidewire mandrel for column support (i.e., support of the balloon against axial compression) typically provide superior pushability relative to systems that rely upon the catheter body for this purpose.
The steerability of a catheter-guidewire system, in general, depends on the ease with which the guidewire can be rotated within a body vessel. This rotational mobility of the guidewire in turn is directly related to the ease with which the guidewire can be rotated relative to the catheter component. The reason is that the catheter component in most guidewire-directed catheter systems is substantially larger in external profile than the guidewire, and hence more difficult to rotate within a body vessel. The extent to which the catheter component must rotate in order to achieve rotation of the guidewire component will therefore affect the rotational mobility of the guidewire. Hence, those systems in which the guidewire component rotates independently relative to the catheter component offer superior steerability.
The original catheter conceived by Dr. Gruntzig is disclosed in Gruntzig, A., et al., U.S. Pat. No. 4,195,637, Apr. 1, 1980. Use of this device was abandoned in the early 1980's following the introduction of "over-the-wire" systems which offered both exchangeability and superior steerability. One such catheter is that disclosed by Simpson, J. B., et al., U.S. Pat. No. 4,323,071, Apr. 6, 1982. The term "exchangeability" denotes the ability of the guidewire and the catheter body to be separated while inside the vasculature for purposes of removing one or the other and replacing the removed component with a substitute component which differs in some respect, the exchange thereby taking place without the need to reestablish intraluminal access.
Although over-the-wire devices remain popular, experience has shown that these devices frequently cannot be advanced through the confines of critical lesions and thus cannot be used to treat such lesions. This limitation led to the development of "non-over-the-wire" systems, which have lower crossing profiles and frequently superior pushability relative to over-the-wire systems, and can thus be advanced within the confines of critical lesions that will not readily accommodate over-the-wire systems.
Non-over-the-wire systems include: (1) "semi-movable" catheter systems, (2) "fixed-wire" catheter systems, and (3) "balloon-on-a-wire" catheter systems. The guidewire components of these systems are permanently held inside the respective catheter tube and balloon components (i.e., the catheter components) of these systems. These systems differ among themselves however in the mobility of the guidewire components relative to the catheter components. An example is disclosed by Samson, W. J., et al, U.S. Pat. No. 4,616,653, Oct. 14, 1986. Fixed-wire catheters permit limited rotational and yet no coaxial mobility of the guidewire components relative to the catheter components. An example is disclosed by Samson, W. J., U.S. Pat. No. 4,582,181, Apr. 15, 1986. Balloon-on-a-wire systems permit no mobility of the guidewire components relative to the catheter components. An example of a balloon-on-a-wire device is disclosed by Crittenden, J. F., U.S. Pat. No. 4,917,088, Apr. 17, 1990.
Non-over-the-wire systems offer several structural and functional advantages relative to over-the-wire systems. Non-over-the-wire systems are generally easier to prepare and easier to advance across critical lesions. Such systems furthermore contain pre-installed guidewires and thus do not require preparation with guidewires. Still further, such systems can be advanced more easily through the confines of critical stenoses due to the lower crossing profiles of these systems and their superior pushability. In some respects, non-over-the-wire systems also offer safety advantages due to their lower shaft profiles: (1) the systems are less prone to provoke ischemia; (2) they are less prone to impair the delivery of medications; and (3) they permit the performance of intra-operative angiography with enhanced resolution.
These attributes have been achieved, however, at the expense of certain others. For example, none of these systems permit separation of the guidewire components from the catheter components. Hence, none of these systems are exchangeable and thus their use obligates sacrificing intraluminal access in the event of an exchange procedure. In the case of selected single-channel fixed-wire and balloon-on-a-wire systems, these attributes further have been achieved at the expense of steerability and structural integrity.
The advantages and disadvantages of selected fixed-wire and balloon-on-a-wire systems vis-a-vis over-the-wire systems relate, in part, to the practice of bonding the catheter component (and in particular the distal balloon component) to the guidewire component in the construction of these systems. Samson, W. J., U.S. Pat. No. 4,582,181, Apr. 15, 1986, discloses a single-channel fixed-wire system that contains one such bond at the distal catheter-guidewire interface. Crittenden, J. F., U.S. Pat. No. 4,917,088, Apr. 17, 1990, similarly discloses a single-channel balloon-on-a-wire system that contains such a bond at the distal catheter-guidewire interface. In these and similar systems, the bond between the balloon and guidewire serves several functions:
(1) It joins the distal aspect of the balloon to the guidewire; PA1 (2) It prevents fluid and gas leakage from the distal aspect of the hydraulic channel and balloon; and PA1 (3) It permits the guidewire to support the balloon against the possibility of axial collapse as the balloon is being advanced through a stenosis.
In short, these bonds enable the construction of air-tight, hydraulically competent, guidewire-directed non-over-the-wire systems with single channels and guidewire-mediated column support. Stated differently, these bonds permit these devices to be constructed with lower shaft profiles and superior pushability relative to over-the-wire systems, which do not contain such bonds and rely upon the respective catheter bodies for column support. For these and other reasons, these bonds are fundamental to the structure and function of selected single-channel fixed-wire and balloon-on-a-wire devices.
Bonding the balloon to the guidewire, however, comprises the steerability of fixed-wire and balloon-on-a-wire systems. This bond tethers the guidewire to the catheter tube as well, and as a result the rotational resistance of both the catheter tube and the balloon is transmitted to the guidewire. This in turn limits the ease with which the guidewire can be rotated within a body vessel, thereby compromising the steerability of the entire composite system. For practical purposes, therefore, the ease with which the guidewire can be rotated relative to the catheter tube in fixed-wire devices such as that disclosed by Samson, W. J., U.S. Pat. No. 4,582,181, Apr. 15, 1986, is limited by the balloon's ability to accommodate torsion. Generally, these devices permit two or three complete (360.degree.) turns of the guidewire in each direction relative to the catheter tube.
In addition to compromising steerability, the presence of a bond between the balloon and the guidewire compromises the structural integrity of single-channel fixed-wire and balloon-on-a-wire systems. In fixed-wire systems, the bond renders the device susceptible to over-wrapping of the balloon. When the guidewire in devices such as those disclosed by Samson, W. J., U.S. Pat. No. 4,582,181, Apr. 15, 1986, is given more than three complete turns in one direction relative to the catheter component, the balloon becomes tightly wrapped over the guidewire. Further rotation of the guidewire relative to the catheter component (and hence the balloon) generates increasing torsion within the balloon and guidewire. This raises the risk of causing tears in the balloon and fractures in the guidewire. To prevent such balloon wrapping and the occurrence of tears and fractures, torque limiters have been developed. An example is disclosed in U.S. Pat. No. 4,664,113 to Frisbie, J. S., et al., May 12, 1987.
The presence of the bond similarly compromises the structural integrity of balloon-on-a-wire systems. These systems typically do not provide any mobility of the guidewire component relative to the catheter component. Directional control of these systems is accomplished by rotating the entire system. During the treatment of critical lesions, the balloon components of these systems can become "hung up" within the confines of a body vessel, and will thus resist rotation. If the operator continues to apply rotational torque to the guidewire in an attempt to overcome this resistance and thereby restore directional control to the system, sufficient torsion may accumulate in the region of the bond to fracture the delicate distal segment of the guidewire or to tear the thin walls of the balloon.
From the foregoing, it is evident that there is a need for non-over-the-wire devices that have the crossing profile and pushability of a fixed-wire or balloon-on-a-wire device and yet afford greater guidewire rotational mobility and hence superior directional control and structural integrity than these systems presently offer, and that are simple in design and amenable to construction by mass production techniques. Such devices would enable one to perform an angioplasty within the confines of critically stenotic lesions with enhanced safety, facility, efficiency and finesse. These and other objects are addressed by the present invention.